1. Field of the Invention
The present invention relates to a surface acoustic wave device including at least one interdigital transducer (IDT) electrode formed by a lift-off method and at least one connecting portion that is electrically connected with the IDT electrode, and in particular, to a surface acoustic wave device further including at least one wiring portion disposed on the connecting portion and a method for manufacturing the same.
2. Description of the Related Art
In recent years, surface acoustic wave devices assembled by a flip-chip bonding system have been widely used in order to reduce the size of surface acoustic wave devices. In this flip-chip bonding system, at least one bump is disposed on at least one pad area in a surface acoustic wave device. The surface acoustic wave device is bonded with at least one connecting area disposed on, for example, a package through the bump. Thus, the surface acoustic wave device is electrically connected and mechanically bonded with the package.
The bump used in the flip-chip bonding system provides not only electrical connection of the surface acoustic wave device to the package but also mechanical fixing of the surface acoustic wave device to the package. Therefore, sufficient bonding strength is required between the bump and the pad area in the surface acoustic wave device. In general, in order to increase the bonding strength between the bump and the pad area, the film thickness of the pad area is increased.
In the surface acoustic wave device, an IDT electrode disposed on a piezoelectric substrate and a connecting portion electrically connected with the IDT electrode are formed at the same time by a lift-off method. Therefore, the connecting portion has the same film thickness as that of the IDT electrode portion. In order to form a bump having sufficient bonding strength, another layer having a predetermined pattern is formed on the connecting portion.
When the IDT electrode, having a fine pattern, is formed by the lift-off method, a resist pattern for forming the IDT electrode is formed such that the cross-section of opening areas corresponding to the fine pattern tapers from the substrate surface to the upper surface of the resist.
Also, the resist pattern of the connecting portion, which is rougher than the IDT electrode, is formed such that the cross-section of opening areas tapers from the substrate surface to the upper surface of the resist. However, as a result of subsequent heat treatment such as baking, the above-described taper, i.e., a reverse-tapered shape, cannot be maintained in the connecting portion having the rough pattern. Consequently, after the resist pattern and unnecessary electrode films are removed by the lift-off method, for example, burring of an electrode occurs at an end of the connecting portion.
Furthermore, another layer having a predetermined pattern is formed on the connecting portion in order to form the bump. Unfortunately, for example, the above-described electrode burring causes a problem such as disconnection on the other layer.
In order to solve the above-described problem, Japanese Unexamined Patent Application Publication No. 2002-261560 discloses the following surface acoustic wave device. The above-described patent document discloses a surface acoustic wave device and a method for manufacturing the same including the steps of forming a connecting portion of a surface acoustic wave element, and subsequently performing etching such that an end surface of the connecting portion has a stair-like shape.
However, the surface acoustic wave device and the method for manufacturing the same according to the above-described related art have the following problem.
According to the above-described patent document, a connecting portion of a surface acoustic wave element is formed, and etching is then performed such that an end surface of the connecting portion has a stair-like shape. In this process, a resist pattern in which the end of the connecting portion corresponds to an opening area is formed on the surface acoustic wave element having the connecting portion thereon. Subsequently, a portion of the end surface of the connecting portion is removed by, for example, submerging the element in an etchant. The resist pattern is then removed to form the desired pattern. The formation of this resist pattern includes the following steps. A resist having a predetermined film thickness is applied, the resist layer is exposed with a photo-mask having a predetermined pattern, and the resultant resist layer is then developed. Unfortunately, this method includes many steps.